1. Field of the Invention
The present invention relates to a system for controlling the aperture in a camera, and particularly to an aperture controlling system which can electromagnetically control the movement of aperture blades to obtain the desired aperture value.
2. Description of the Prior Art
There is known a camera containing an automatic aperture control mechanism which electromagnetically controls the aperture for an objective lens, the automatic aperture control mechanism being actuated in shutter speed priority mode or program mode to control the exposure. In the general single-lens reflex cameras, such mode control is made in accordance with one of two following photometric methods. One of these photometric methods is the full aperture metering system in which when the aperture is automatically controlled in the shutter speed priority mode, the shutter will be actuated at a manually preset shutter speed and the aperture will be controlled to provide a proper exposure corresponding to the preset shutter speed. If the controlled aperture value is improper, the proper exposure cannot be obtained when the automatic aperture control is made in the shutter speed priority mode. In accordance with the other metering system, an aperture value providing a proper exposure corresponding to the manually preset shutter speed is computed. The aperture is then controlled into the computed aperture value. The shutter is operated at a shutter speed to provide the proper exposure based on the amount of light passed through the controlled aperture. If the controlled aperture value agrees with the computed value, therefore, the same shutter speed as the preset shutter speed is reproduced to effect the control in the shutter speed priority mode. If the controlled aperture value is not consistent with the computed value, the shutter is actuated at the shutter speed providing the optimum exposure corresponding to that aperture value so that the desired exposure can be attained. Since this shutter speed is different from the preset shutter speed, however, such an operation mode is not exactly the shutter speed priority mode. This holds true of the program mode.
The improper control of the controlled aperture value into the computed value in the automatic control system results from time delay in the latching operation of an electromagnetic latch mechanism in the aperture control system. Error due to this time delay can be eliminated by adjusting the latch mechanism to provide an electric latch signal at an earlier time if the aperture to be latched is constantly operated with the passage of time.
In interchangeable lens cameras, however, the aperture mechanisms for the interchangeable lenses are different from one another in spring load and inertia load. Since the characteristics in the aperture mechanisms are transmitted to the aperture latching mechanism in the camera, the variable characteristic of the aperture value relative to the passage of time will be different from one interchangeable lens to another. It is thus very difficult to provide a properly controlled aperture value for each interchangeable lens by the fact that the relationship between the time delay in the electromagnetic latch mechanism and the variable characteristic of the aperture value relative to the passage of time is variable.